1. Field of the Invention
The present invention is directed to an improved method and apparatus of fingerprinting, and more particularly to a method and apparatus permitting the inkless recording of fingerprints without any attendant staining of the fingers with ink or highly colored chemicals.
2. Description of the Prior Art
The art of fingerprinting and identifying persons by their fingerprints is well known. The simplest method of taking a person's fingerprints is to apply a highly colored ink or dye to a person's finger tips. Subsequent rolling or pressing of the person's fingers on a clean recording surface, such as paper, deposits the ink or dye on the surface in a pattern corresponding to the fingerprints of the person. While the above simple method has been widely accepted and used by law enforcement agencies and the like, commercial application of fingerprinting has been greatly hampered by the understandable reluctance of people to have their fingers stained by the application of a highly colored ink or dye.
In addition the inherent lubricity of currently used petroleum based inks often causes a relative slipping between the fingers and the ink film. As a result an undesirable smudging or smearing of the fingerprints may occur.
In order to overcome the problem of stained fingers, the prior art has developed a number of methods and devices wherein the risk of having the person's fingers stained by a highly colored chemical or dye is reduced. Such devices, generally termed inkless devices, usually utilize two substantially colorless chemical reagents. The first chemical reagent is applied to the fingers of the person to be fingerprinted. The person then rolls his fingers on a piece of paper or other suitable recording surface, thereby depositing the first chemical reagent in a pattern corresponding to the fingerprint image.
In some prior art devices such as the one disclosed in U.S. Pat. No. 2,299,652, the paper is impregnated with a second chemical reagent. In some other devices such as for example in the one disclosed in U.S. Pat. No. 3,960,632, the paper having the first chemical reagent deposited thereon in a latent fingerprint image is sprayed with the second chemical reagent. The first and second chemical reagents in both instances are selected to react with one another to form a highly colored, preferrably dark blue or black substance. The latter develops on the surface of the paper in a pattern corresponding to the fingerprint of the person. Thus, in this manner the fingerprint can be recorded without subjecting the person to the inconvenience of staining his fingers.
The principal requirements for these chemical reagents suitable for inkless fingerprinting are that they be relatively inexpensive, non-toxic, adaptable to storage and are easily applied on the fingers. Furthermore, the rate of the chemical reaction between the reagents should be sufficiently rapid so that the development of the visible fingerprint image can be readily monitored and a determination be made whether a satisfactory image has been obtained. A relatively large number of suitable chemical reagent pairs for this type of application is disclosed in U.S. Pat. No. 2,235,632 as well as in U.S. Pat. No. 4,029,012. U.S. Pat. No. 4,029,012 discloses the use of ferric chloride and 8-hydroxyquinoline solutions in a two-part inkless applicator particularly adapted for quick recording of thumbprints. Additional disclosures relevant to inkless fingerprinting devices can be found in U.S. Pat. No. 3,755,517; U.S. Pat. No. 3,447,818; U.S. Pat. No. 3,851,619 and in British Printed patent specification No. 428,386.
While the prior art inkless fingerprinting devices have solved some of the problems associated with traditional fingerprinting, the prior art inkless devices still generally suffer from the following drawbacks. As a person's finger, having a first chemical reagent thereon, is pressed to a paper surface containing the second chemical reagent, the finger still may be stained by the colored substance which is instantaneously formed as a result of the chemical reaction between the first and second reagents. Spraying the paper sheet with the second chemical having the essentially invisible fingerprint pattern deposited thereon eliminates the above problem. However spraying is a messy procedure and subjects the operator of the fingerprinting device to the risk of possible long term exposure to the second chemical which is freely dispersed by the spray.
It has been suggested in U.S. Pat. No. 2,235,632 that the essentially invisible fingerprint deposited from the person's finger on the paper may be developed by a colorless powder or volatile vapors comprising the second reagent. U.S. Pat. No. 2,235,632 describes a number of substantially colorless chemical reagents or mixtures thereof, which after having been deposited on the surface of the paper may be transformed into a highly colored substance by the application of heat or intense light. However, the application of heat or intense light suffers from the obvious disadvantage that additional appendages to the fingerprinting device such as a heat or a light source may be required. Furthermore, the operator of the fingerprinting device cannot immediately judge whether or not the fingerprint taken is acceptable, since he has to wait until the fingerprint is developed by the application of heat or light.
Developing of the invisible fingerprints by exposure to volatile vapors of the second reagent, as suggested by U.S. Pat. No. 2,235,632, appears to provide certain advantages. However this method has not gained acceptance in the prior art and U.S. Pat. No. 2,235,632 failed to teach specific examples of chemical reagents which are suitable for this type of application in a fingerprinting device. Furthermore most chemical reagents having a sufficiently high vapor pressure at room temperature to enable this type of application comprise gases or volatile liquids. It is readily understood that utilization of a gaseous chemical reagent or of a volatile liquid in a simple, inexpensive and compact fingerprinting device is undesirable. Use of such reagents would not only be impractical but would also increase the risk of exposing the operator of the device to the long term, possibly toxic effects of these chemicals.
For the above stated reasons a need still exists in the prior art for a simple, compact, reliable and inexpensive inkless fingerprinting device. Such a device must not unduly expose its operator to toxic chemicals and must eliminate the possibility of staining a person's fingers with highly colored chemicals.